High temperature superconductors, that is, superconductors that have a critical temperature on the order of 90.degree. K., are disclosed by Wu et al , Phys. Rev. Lett. 58, 908-910 (1987). These high temperature superconductors are based on the Y--Ba--Cu--O system. U.S. Pat. No. 4,929,594 discloses a superconducting composition comprised of a crystalline phase of the formula Tl.sub.2 Ba.sub.2 CuO.sub.6+x, wherein x is from 0 to about 0.5, that has a temperature above 90.degree. K. Subramanian et al., Science 239, 1015-1017 (1988), disclose materials of the formula Bi.sub.2 Sr.sub.3-x Ca.sub.x Cu.sub.2 O.sub.8-y which show a resistivity drop at about 116.degree. K. and apparent zero resistivity at 91.degree. K.
A wide variety of applications for superconducting materials has developed. These applications include power transmission and high-speed computer electronics. Superconductor materials have been used primarily in the form of sintered articles since elongated articles such as wire are difficult to form and have non-uniform properties. Known technologies of forming super-conducting wire, as shown in U.S. Pat. No. 4,980,964, employ powder-in-tube technology. This technology entails filling a metal tube with a powder of super-conductive material, sealing the tube, and cold drawing the sealed metal tube until a predetermined wire size is achieved. The drawn wire is heat treated to assure crystallinity in the superconductor material. This technology, however, produces wire of short lengths and nonuniform properties.
An improvement over powder-in-tube technology is described in European Patent Application publication number 0 292 385. This publication describes manufacturing an elongated superconducting composite by kneading a mixture of powder of superconducting oxide with a binder while shaping the resulting kneaded paste into an elongated pre-form by an extruder or other device. The pre-form is heated continuously to remove the binder. The pre-form then is wrapped with a metallic sheet and sintered at elevated temperatures. While this method results in longer and somewhat more uniform superconducting wire, this method can change the phase content of the resulting sintered ceramic and thus sacrifice superconducting properties.
European Patent Application 306,034 shows a method of forming superconducting ceramics which have a metal cladding thereon. In an embodiment, preforms of plastic compositions of polymer, plasticizer, and ceramic material are bonded prior to firing with a blend of metal, polymer and plasticizer to yield a metal clad sintered ceramic article upon firing. This method, however, is susceptible to undesirable leaching of materials between superconducting material and the metal coating. Also this method uses less than 10% of polymer and a plasticizer causing a high void content in the superconducting oxide and thus lower performance.
A need therefore exists for processes for manufacturing elongated superconducting ceramic, metal clad articles useful for wire application which provides increased lengths and uniformity, and high density ceramic superconductors but which avoids the deficiencies of the prior art methods.